This invention relates to new surface-active polymers and to their use for the direct production of polyurethane powders from the components in an organic carrier phase.
Polyurethane powders and their use on an industrial scale are known. The powders are normally expensively produced by grinding of corresponding granulates. Direct synthesis of the powders from the components in an organic carrier phase by suspension polymerization is much more economical, the best results being obtained when aliphatic and/or alicyclic hydrocarbons are used as the carrier phase.
Surface-active auxiliaries are essential for carrying out this direct synthesis. The function of the auxiliaries is to convert the reaction components into finely divided emulsions and to keep the polyurethane formed in emulsion or suspension until the reaction is over.
Special polyoxyalkylene/polydimethylsiloxane graft or block copolymers are proposed in German Auslegeschrift 2,816,170 as surface-active auxiliaries for the direct synthesis of polyurethane powders in a carrier phase of aliphatic hydrocarbons. However, polydimethyl siloxane-containing polymers are generally not favorable for polyurethane applications because they readily lead to surface defects in the moldings and to difficulties during painting, so that quantitative removal of these auxiliaries from the powder is essential. German Auslegeschrift 2,456,927 describes block or graft copolymers of polylactones and long-chain alkyl esters of (meth)acrylic acid and corresponding products of polyoxyalkylene glycols and long chain alcohol esters of (meth)acrylic acid as surface active auxiliaries for the direct production of polyurethane powders by suspension polymerization in a carrier phase of aliphatic hydrocarbons. These auxiliaries have the disadvantage that they are OH-functional and are thus incorporated in the polyurethane produced, which can result in changes in the mechanical properties of the products and, in addition, makes it impossible to reuse the auxiliaries.
German Auslegeschriften 2,556,945, 2,559,769 and 2,442,085 and U.S. Pat. Nos. 4,032,516 and 3,787,525 describe copolymers of N-vinyl pyrrolidone and long-chain .alpha.-olefins as surface-active auxiliaries for the direct synthesis of polyurethane powders in a hydrocarbon carrier phase. These auxiliaries cannot be incorporated, but are not easily desorbed from the surface of the powder formed so that elaborate washing operations are necessary to recover the auxiliaries.
The problem addressed by the present invention was to provide improved copolymers. Another problem addressed by the invention was to provide a process for the direct production of polyurethane powders which gave finely divided polyurethane dispersions and in which the emulsifiers used could readily be removed after formation of the powders.